Process for manufacturing a layer of yarns, via stitches, in particular for the production of composite material parts

ABSTRACT

A process for producing a layer of yarns grouped into rovings, via stitches, on a base, in particular for the production of composite material parts, by inclusion of the rovings in a matrix. The process includes carrying out the steps of depositing at least two rovings on the base, and stitching the at least two rovings thus deposited on the base with at least one stitch comprising two stitch holes.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims the benefit of the International Application No. PCT/EP2019/070516, filed on Jul. 30, 2019, and of the French patent application No. 1857128 filed on Jul. 31, 2018, the entire disclosures of which are incorporated herein by way of reference.

FIELD OF THE INVENTION

This invention relates to a process for manufacturing a layer of yarns, via stitches, in particular for the production of technical parts, in particular of composite material parts.

BACKGROUND OF THE INVENTION

Machines are known, more particularly embroidery machines that can make stitches on a base, for example a layer of woven yarns.

These embroidery machines can follow any type of programmed pattern.

Thus, on a base, the base being integral to a defined support which stretches the base, the rovings of another material, for example, are deposited.

For the rest of the description, “roving” will be defined as a group of unidirectional threads or fibers, whether or not wrapped, twisted or not, the threads or fibers forming a bundle, the threads or fibers being made up of different types of materials, possibly impregnated. It can even be a woven ribbon with an integrated matrix.

More generally, any thread-like product can be treated by using the process according to the invention, such as a ribbon, tube, optical fiber, etc.

This definition of “roving” is used to avoid confusion of vocabulary with “yarn stitching.”

This roving is distributed by a head on the base following a programmed pattern that can be rectilinear, curved, or a combination of the two to follow a complex geometrical pattern.

This roving thus distributed on the base must be attached by a stitch in order to preserve the geometrical patterns of the deposit.

These geometrical patterns can, for example, be used to arrange reinforcements on a base in perfectly circumscribed areas to make dry preforms to produce technical parts, more particularly of composite materials, by embedding this preform in a resin matrix, for example, which the process uses in a mold with resin injection, or a bladder for resin infusion under pressure. The technique selected may also provide for pre-impregnation introduced into a mold, the final implementation technique not affecting the process of this invention, which applies to all these techniques.

This process makes it possible to produce parts with very precise reinforcements, thus limiting the consumption of raw material, limiting the weight, and positioning the reinforcements precisely.

This process allows for production especially in small and medium series with limited costs due to necessarily limited labor because the fibers are deposited automatically; changes in the type of rovings are also made possible like the color threads on an embroidery machine.

SUMMARY OF THE INVENTION

An objective of the process according to this invention is to increase the productivity of roving deposits with the same sewing speed, i.e., the same number of stitches and the same stitch length. This goal is reached by limiting the directional changes which are disadvantageous for the machines because it is necessary to overcome the inertia related to the movement of the base support plate, this plate being mobile under the head of the roving deposit and stitching of the rovings.

In fact, whatever the mode and the mechanical means of operation in both horizontal and vertical movement of the support plate, inertia is still a problem that must be overcome.

When they are micromotors, the problem also occurs.

BRIEF DESCRIPTION OF THE DRAWINGS

The process according to this invention is now described in detail according to a particular non-exhaustive mode of production, with reference to the attached figures, figures that represent:

FIG. 1 is a view of a layer of a single roving illustrating the deposit of the prior art,

FIG. 2 is a view of a layer of at least two rovings according to the process of this invention, with stitching of each of the at least two roving s, illustrating the deposit of the prior art,

FIG. 3A to 3C are synoptic of deposit with a rotating head,

FIG. 4 is a view of a layer of at least two rovings according to the process of this invention, with stitching of the set of at least two rovings,

FIG. 5 is a view of the layer with a half rotation of the continuous rovings,

FIG. 6 is a view of the layer of several rovings, of varying sizes.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a single roving 1, deposited on a base 3, this roving being joined by a stitch 5 comprising continuous zigzag-type stitches 5-1, 5-2, 5-3.

The support plate of the embroidery machine houses the base 3 on which is deposited there at least one roving 1 from a depositing and sewing head, not shown, the device being commercially available.

This sewing and depositing head comprises two parts, a depositing head, and a sewing head, which are placed side by side. The depositing head deposits at least one roving on the base and this depositing head is mobile in rotation while the sewing head has a needle fed by a sewing stitch, fixed in rotation and mobile in vertical movement, this in a known way.

A single roving is deposited and the stitches are on either side of the single roving, alternating; when this type of zigzag stitch is intended, the stitch provides for a change of direction.

It is understood that the sole purpose of the stitching is to mechanically hold the roving on the base in order to retain this roving in the chosen and necessary position on the base according to the technical part to be made subsequently from the base supporting its rovings, according to a given geometrical distribution.

This stitching does not necessarily intervene mechanically in the intrinsic qualities of the product since the weave is then embedded in a resin matrix or molded using pre-impregnated rovings, for example, and more generally regardless of the method used.

The positioning and the follow-up of the geometry of the deposit are essential so that the finished product has the rovings with the necessary positioning for the resumption of the efforts, in particular, in the chosen directions.

In FIG. 2, the process according to this invention provides for stitching of a set of rovings, comprising at least two rovings, namely three rovings M1, M2 and M3 with stitches S1, S2 and S3, i.e., four stitch holes p1 and p4, in alignment with each of the rovings, the change of direction being carried out only on the outer edges of the set of rovings, i.e., on the outer edges of the at least two deposited rovings.

Thus, in FIG. 2, three stitches S1, S2 and S3 are provided for three rovings, each roving being held between two stitch holes, M1 between p1/p2, M2 between p2/p3 and M3 between p3/p4. It can be seen that the change of direction of the base plate 3 with respect to the depositing and sewing head, i.e., the direction of rotation of the rotating depositing head, is performed at stitch holes p1 and p4, with the three stitches S1, S2 and S3 aligned in the same direction.

In the case of a rotating depositing and sewing head, as shown in the synoptic diagram in FIG. 3, it can be seen that, in FIG. 3A, the first stitch hole p1 is made on the upstream edge in the direction of movement of the depositing and sewing head, i.e., on the outer edge of the first roving M1, to be deposited exteriorly; the first roving M1 is deposited and the second stitch hole p2 is made on the downstream edge of the roving M1, transversely due to the advancement of the base support plate and the time of deposit of each roving in the interval between two stitch holes.

This leads to a stitching inclined with respect to the direction of the rovings.

This second stitch hole p2, FIG. 3B, is on the upstream edge of the M2 roving to be deposited. The stitch hole M2 is deposited and the third stitch hole p3 is made on the downstream edge of the roving M2. The third stitch hole p3 is on the upstream edge of roving M3 which is deposited in order. The fourth stitch hole p4, FIG. 3C, is carried out on the downstream edge of the roving M3, after its deposit, thus on the external edge of the set of rovings.

The change of direction is carried out at stitch p4 for a new series of deposits of the three rovings M1, M2 and M3 of the set of rovings with new stitches and stitch holes p1′, p2′, p3′ and p4′ respectively.

Each of the M1, M2 and M3 rovings is thus perfectly positioned and, for six stitch holes, the depositing and sewing head have to manage only one change of direction on each outer edge of the set of rovings, instead of the five that would have been necessary with the prior art, not counting the starting point to return to the outer edge of the M1 roving.

The stitch is thus of the zigzigzig/zagzagzag type.

In FIG. 4, a variant comprises arranging a set of at least two rovings, in this case three rovings, M1 to M3 by making a single stitch S1, from the outer edge of the first roving M1 with a stitch hole p1 to the outer edge of the at least second roving lock, in this case the third roving M3, with a stitch hole p2.

In fact, the three rovings M1, M2 and M3 are held by a single stitch and the change of direction occurs again only on the outer edges of the set of rovings.

In FIG. 5, the problem of stitches is addressed when a reversal is performed to turn the rovings back and deposit across the feed direction of the base 3. The support plate receiving the base 3 ensures step-by-step feed in the selected mode of production, the step corresponding to the width of the set of rovings, for example, so that all the rovings are spaced at the same distance from each other.

Indeed, when the set of rovings reaches the edge of the base 3, it is necessary to make a half turn at 180° to come back and deposit the set of rovings parallel to the first deposit, in a known way.

If you wish to deposit the same quantity of material and if you want a perfect repetitiveness of the successive deposits, it is necessary to proceed to an adapted stitching in the reversals.

The aim is to respect the alternation M1, M2, M3/M1, M2, M3 in both directions of application, while limiting direction changes.

Thus, the stitch holes p1 to p4 are made along almost straight lines in the inversions, with stitches of almost the same length and with identical consumption and length of M1, M2 and M3 rovings.

This provides a homogeneous density of rovings deposited on the base and therefore a balanced density of fibers in the composite material product that will be made with this layer of yarn.

Also, the bending radius is the same for all the rovings, which in some types of rovings is an important advantage, thus avoiding bending radii that are too small.

This is even more important if we imagine a solution in which the rovings from the same set are different. The length of the deposited rovings is thus identical.

It is also possible to vertically superimpose two or more of the rovings on a length L, from the same set when necessary, in order to provide reinforcement or to create a fiber-free zone that will be perforated, in order to preserve the continuity of the fibers of the different rovings.

It is even possible to use M1 in place of M3 and M3 instead of M1.

This guided deposit of several rovings simultaneously ensures faster work and an embroidery machine can be used to make such a layer of yarn. The deposit has been described on the basis of the use of a rotating head but a comb could also be used.

The precision and computer control also makes it possible to compete with other existing processes and devices. The stitch mentioned is of the zigzag type but it could be of the three-sided zigzag type to form not triangles but rather rectangles.

It also ensures the reliability of the embroidery framework due to the precision of the embroidery head movements.

It is also possible to produce a series of stitches and to provide a spacing between the series of stitches.

This is described in relation to an embroidery machine with a rotating head, but a movable head would provide exactly the same result.

While at least one exemplary embodiment of the present invention(s) is disclosed herein, it should be understood that modifications, substitutions and alternatives may be apparent to one of ordinary skill in the art and can be made without departing from the scope of this disclosure. This disclosure is intended to cover any adaptations or variations of the exemplary embodiment(s). In addition, in this disclosure, the terms “comprise” or “comprising” do not exclude other elements or steps, the terms “a” or “one” do not exclude a plural number, and the term “or” means either or both. Furthermore, characteristics or steps which have been described may also be used in combination with other characteristics or steps and in any order unless the disclosure or context suggests otherwise. This disclosure hereby incorporates by reference the complete disclosure of any patent or application from which it claims benefit or priority. 

1-6. (canceled)
 7. A process for producing a layer of yarns grouped into rovings, via stitches, on a base for production of technical composite material parts, comprising carrying out the following steps: depositing at least two rovings on said base, and stitching the at least two rovings thus deposited on the base, with at least one stitch comprising two stitch holes.
 8. The process for producing the layer of yarns grouped into rovings according to claim 7, wherein the stitches are aligned, each roving receiving a stitch hole on either side.
 9. The process for producing the layer of yarns grouped into rovings, according to claim 8, wherein the stitch holes are aligned.
 10. The process for producing the layer of yarns grouped into rovings, according to claim 7, wherein the stitching is slanted in a direction of the rovings.
 11. The process for producing the layer of yarns grouped into rovings, according to claim 7, wherein, when inverting, the rovings are placed alternately and lengths of the deposited rovings are identical.
 12. The process for producing the layer of yarns grouped into rovings, according to claim 7, wherein at least two of the at least two rovings are deposited superimposed over a length. 